Which one of the following is a food preservative ? Equanil, Morphine, Sodium benzoate.

Explanation

To determine which of the given options is a food preservative, we will analyze each option based on their properties and uses.

### Step-by-Step Solution:

1. **Understanding Food Preservatives**:
- Food preservatives are substances added to food to prevent spoilage caused by microorganisms, thus maintaining the food's nutritional value, taste, and smell.

2. **Analyzing the Options**:
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